Analog switches target feature-rich cell phones

San Mateo, Calif.  To address wireless handsets with lots of multimedia features, Fairchild Semiconductor International last week introduced a family of analog switches designed to increase audio quality while switching signals among three or more outputs. The family of three parts  the FSA4157, FSA1156 and FSA1157  evolved from Fairchild's FSA3157, which the company claims is the switching standard in today's cell phones. The new parts reduce RDS(on) to 1 ohm, with total harmonic distortion of 0.002 percent and an operating range from 1.65 to 5.5 volts.

Paul Kierstead, director of corporate marketing at Fairchild (South Portland, Maine), said the significant reduction in RDS(on) results in a "less lossy" switch and less burden on system power to drive a speaker. In addition, on-resistance flatness of 0.2 * helps minimize total harmonic distortion, which in turn helps preserve audio signal quality during switching.

"Cell phones are getting much more feature- and media-rich, with Hi-Fi audio, color screens and graphics, and, in some cases, physical interfaces to other devices," Kierstead said. "We need to make analog switches with much lower losses and higher fidelity to support that."

The analog switch market represented $156 million in revenue in 2002 and is expected to reach $262 million by 2007. Over the last three years, Fairchild's analog switch group has experienced robust growth  even as the segment declined 14 percent  and ranked as the fourth-largest analog switch supplier in 2002, behind Maxim, Vishay Siliconix and Analog Devices, according to Selantek Inc. (Mountain View, Calif.).

Kiersted attributed the performance to Fairchild's orientation toward sub-5-V products, which are in demand as analog switch use increases in cellular handsets and other portable applications. Selantek estimates that cell phones currently consume 51 percent of analog switch units.

The FSA4157 is a single-pole/double-throw switch, while the FSA1156 is a normally open single-pole/single-throw, and the FSA1157 is a normally closed single-pole/single-throw. The devices have more than 350-MHz bandwidth and offer electrostatic discharge protection of 7,500 V.

Kiersted said that the wide voltage range of Fairchild's analog switches gives customers greater application coverage with a limited inventory of part numbers, while BiCMOS circuit design techniques eliminate the characteristic performance trade-offs.

The new parts are available on a four-week lead time and are housed in lead-free, six-lead MicroPak and SC70 packages. The FSA4157 sells for 45 cents, and the FSA1156 and FSA1157 are priced at 38 cents. Pricing is per unit based on quantities of 1,000.